1. Field of the Invention:
The present invention relates to thermal resistivity coatings for optical fibers, particular coatings resistive to light and heat energy incident from a laser.
2. Description of the Prior Art
Coatings for mechanical and fire protection of optical fibers are known per se. Representative of the prior art constructions include U.S. Pat. No. 4,089,585 (Slaughter et al.) which discloses coatings of plastic materials (e.g. nylon, polyurethane, polyvinyl acetal enamel) and also metallic coatings, such as aluminum and aluminum based alloys; U.S. Pat. No. 4,645,297 Yoshihara et al. (various fiber-reinforced resin compositions); and U.S. Pat. No. 4,653,851 (Pedersen et al.) (alternate layers of mica and synthetic materials such as Kelvor). Silicon acrolate also has been used as a coating for optical fibers.
However, optical fibers previously largely have been used in communication applications where the fibers are in an environmentally protected enclosure. Damage by lasers is not a subject of concern in such conventional applications; therefore, protection against laser damage has not been provided. Currently, optical fibers are used or proposed for use on weapon systems such as the Fiber Optic Guided Missile (FOG-M). One countermeasure for such systems will be to cut or damage the optical fiber by subjecting the fiber to a beam from a high energy laser. Optical fibers are not generally protected against thermal radiation and would therefore fail, causing the loss of the missile.
FIG. 1 depicts a possible laser-based countermeasure to an optical fiber guided missile. In FIG. 1, Fiber Guided Missile (FOG) 12 under control by communications with user 14 scans for target 16. High energy laser 18 mounted on vehicle 20 uses a scanning motion to cover the sector from which FOG 12 originates. Laser beam 22 damages optical fiber 24 as it passes over the fiber. Analysis shows that for a scan rate of 10 Hz at a range of 2 km from the fiber, a 4.5 MW laser would cut currently used optical fibers with plastic outer layers, where the outer layer is a covering of the silicon acrolate type. This laser power level is well within the state of the art. It is anticipated that methods to detect deployed optical fibers will be developed in the future and thereby permit a more accurate placement of the laser beam on the fiber. This will greatly reduce the laser energy required to damage the fiber, making optical fiber guided weapons even more vulnerable.
While there is no known technique identified to protect the fiber against laser damage where the laser beam is maintained on the fiber for an extended period of time, it is believed that protection can be provided for the condition where the laser beam is scanned to provide an umbrella of protection to targets. Scanning requires that a large area be covered by the laser beam with a resultant short dwell time on a particular fiber.
It is, therefore, an object of the present invention to provide a protective coating for an optical fiber especially suited for protection against an intermittent incident laser beam.
It is also an object of the present invention to provide an improved coated optical fiber construction for streaming deployment from missiles and the like for use in environments where sweeping laser beams may be encountered.